Blood pressure changes after high- and low-salt diets: are intermittent arm measures and beat-by-beat finger measures equivalent?

The assessment of sodium sensitivity requires to measure the difference in mean arterial pressure (map) at the end of sodium-loading (sload) and sodium-depletion (sdepl) maneuvers with an arm-cuff manometer. aim of this study is to evaluate whether map measuring devices based on the volume-clamp method at the finger can also be used for assessing sodium sensitivity. sixty-eight normotensive volunteers underwent sload and sdepl diets in random order. map was simultaneously measured at the end of each diet with arm (spacelabs 90207) and finger (portapres model-2) cuff devices. the sodium sensitivity was assessed as the difference in map at the end of sload and sdepl diets (δmap), and as salt-sensitivity index (ssi; ssi=δmap divided by the difference in urinary-sodium-excretion rate at the end of the diets). discrepancies between finger and arm-cuff devices in δmap or ssi were evaluated by bland and altman analysis. even if discrepancies between devices had null-fixed bias, results showed a significant proportional bias and large limits of agreement (between −25 and 25 mm hg for δmap, between −196 and 180 mm hg mol−1 per day for ssi). the ssi distribution over the group was larger, flatter and less symmetric if derived from finger-cuff rather than arm-cuff devices, and this influenced substantially the identification of salt-sensitive individuals. therefore, the response of map to sload/sdepl diets and consequently the assessment of the salt-sensitivity condition depends importantly on the measurement site, and brachial measures should be preferred for consistency with literature and normative data.